Combined heating electrodes and variable capacitor for dielectric heating



Apr! 25, 1950 w. L. ATWOOD 2,504,956

COMBINED HEATING ELECTRODES AND VARIABLE CAPACITOR FOR DIELECTRIC HEATING Filed May 31, 1946 2 Sheets-Sheet 1 E l INVENTOR a MA F/P/D 1. #711000 BY (JUL, chi u/vw ATTORNEYS April 25, 1950 2,504,956

W. L. ATWOOD COMBINED HEATING ELECTRODES AND VARIABLE CAPACITOR FOR DIELECTRIC HEATING Filed May 31, 1946 2 Sheets-Sheet 2 INVENTOR 1/44 F/Wp Z. 4%;1 000 wildwi M M ATTORNEYS i 'atented Apr. 25,

COMBINED nnAT NG ELECTRODESlANIi VARIABLE CAPACITOR FOR .DIELE'C'J TRIC HEATING Wilma L; Atwood, ,Newton Lower -Falls, Mass;

assignor 110 Jfhefiirdler-Corporation, Louisville, Ky.-,. a corneration of Delaware Application' May 31, 1946,"Serial No: 673,296

11i.Claims.. (Cl. 219-47) This invention relatesto highfrequencytreating'systems for dielectricmaterials and hasfor an object the provision "of-means not only of applying'pre'ssure to"the1oad*'or-to the dielectric roaterial undergoii'ig treatniembut also for regu lating the "amountof electrical power or 7 energy applied'to "or absorbedby said material.

Ithas heretoforebeen recognized that dielectric materials change their characteristics with increasing temperature: The powerfactor and dielectric constant of man-y materials increase as the temperature rises: In accordance with the disclosure of myco -"pendingapplication, Serial N0i'5'97,048, filed. June- -1,' 1945,*f0r- High-frequency' treating" system, therelative positions of the heating electrodes-are automatically varied to maintain the electrical energy'delivered to the 1oa'd"'o-r' the material tolee-heated at apredetermin'edf'or constant value-. A-system of' that ch aracter'imgeneral requires thatthere'bemai-n tain'edaspace between at least one-'of'theelec' trodes'and the material undergoing treatment; 1

In carrying out thepresent invention in oneform thereof; a'systenris prcvidedwvhichmay.

function 'inthe same manner as-the system of my said co-pending-application': Addition-ally, .apressureplate or el'ectrode-*is provided for en-: ga'gem'en't with the work orthe" material to be heated and" b'y*mean's-0f which-pressure may-be exerted thereon" during the "heating" operation?- With this electrode direetl-yumcontact with the material to be heated, another-electrode may-be adjustedtowary the-- capacitance in'theheating circuit to maintain the power input 1evel--'- substantiallyconstant-atapredeterminedvaluenotwithstanding changes in the dielectric constant and in" the resistance ofthe load comprisingthe material undergoing treatment? In accordance with theinvention, theusefulness of myprior system is extended and the new system may be" used for a variety of l'h'eating problems, either with or without the applicationofpressure to the material to be heated.

For a moredetailed presentation of the invention and: for further objects and advantages thereof reference should-be had to thefollowing description taken in conjunction With-the accompanyingdrawings in which:

Fig. 1 is-a sectionalview, of aniappar-atus em,-

bodying the invention,taken OllnthB line l-i of i Fig. 2.5with parts added;

Fig. 2 is asectionaliview takenon the line 2.--2 OfJFig; 1'- with part's omitted; and

Fig. 3 is awiring diagram; diagrammatically illustrating the principal cles.

any; change. 1n the capacitance betweenthe; two

setseof; electrodes. A1change in themapacitance.. ofithetank or output circuit produces achange tern embodying the invention.

Referring to the-schematic wiring diagram of Fig.=' 3, there is-i1lustrated the load ormaterial i ete-betreated'as disposed between'a lower-elec trode I l and-- an upper electrode- I A third electrode" l3 is connectedto a conductor-4 4 dead ing to an output coilor'inductor -I 5,-"which through a blocking -capacitor It is =connected to the anode of the eleotric'valve I'L The anode of -the :va1ve-- ectedthrough a choke coil v1 lfl -to the" Side of asource of anode voltage,- the negative side thereofi being connected by way ofi '5 4 is :cosr positiv a --plate-current meter. l 9 =to ground andbya con-.

, ductor Qu te the mid p'oint oi the-secondaryavind,

ing. of a filament -transformeix 21; .theiprimaryu.

' 1 g of which isconnected to a suitablesourceof alternating-current supply; The egridiof thee valve H is connected bylacgrid. coil 22 through agrid-leak resistor '23 anduasgride'leak capacitor;

Mite-the conductor; 26. leading :to. the cathode.

Theemeter I9 is not :included irraithe'hgrid. circuit. since the conductor- ZGLis connected-.1 above. the; groundeduside ofmeter 19;: Thecircuitmay be.

driven or excited by voltage applied.by-wa v of. the anode-gridcapacitance, as; indicated :.b.y the capacitor 2 licshown. by; the: dottedlines. or 4: the grid circuit maybe driven by, inductive coupling.. with the output or-anode. inductonlfi; Thegcir i cuit parameters are:.selected sozthatthecapaci-b tancebetWeen theeelectrodes 1| 1 and. ;i 2; and bee tween the electrodes; i 2 and 13,2 will; withtheim ductance 0f. the inductor. 95, :be. resonant, at. a. desired .operatingfreq-uency which will ordinarily lie inthe range-of from 1 tO,: 3D or;m0re,megacy+ Since thev grid .1 circuit a, is; energized from; they anode or output ;cir.cuitwhich. includessthe.

load or thedielectric material it]; it ,willbeunderstood that the'frequency. ofgthe-energy, supplied.

to. the grid circuit wil-Lvary inaccurda-nce; with in. the resonant frequency; thereohbutthe grid. circuit while changedgysomewhatg,only: produces slight changes yinthe available power in 171131101..- mal range of. operation becauseof. a. change, in

frequency. However; the power-suppliedbythe; oscillator will .belargely. dependent upon the volt-5: 3? age appliedttothe: load; I 0, and :thiss-voltage will;

vary: with: the: spacing of; the. several electrodes;

In accordance with: the present invention; a motor 38; under manualor automatic control, is energized:to move the eleotrodez l2-'into;.engagementwith; the work. or'material: W. A second;

- components of a sysmotor 3!, suitably connected to the electrode I3, will, under manual or automatic control, be energized to produce the desired spacing between the electrodes i2 and 13; that is, a spacing which will apply across the load H) a voltage oi desired magnitude. Since there are effectively present in the output circuit two capacitors, Ill2 and i2lt, in series, the voltage across them will divide inversely as their respective capacitances. Accordingly, as the electrode I3 is lowered to decrease the spacing with respect to the electrode 22 and to increase the capacitance, the voltage between the electrodes II and 12 will be correspondingly increased. Conversely, opposite movement of the electrode l3 to decrease the capacitance between it and electrode l2 will produce a decrease in the voltage applied to the load or material disposed between electrodes H and 12. Accordingly, any desired percentage of the output voltage of the oscillator or high-irequency generator, including the electric valve Il, may be applied to the material Hi.

In the preferred form of my invention, the lower electrode ii, Fig. 1, preferably comprises a slidable tray having a handle Ha by means of which it may be withdrawn or inserted in a cabinet iractionally illustrated as at 32 and 33. The cabinet is arranged to house the circuit components partly illustrated in Fig. 3 and which include the output coil or inductor 15 which, it will be observed, is mounted on insulators 3 3 secured to a shelf or dividing wall 35. One end of the coil i is connected to ground, i. e. to the wall 35. The electrode i2 is carried by four insulators, two of which, the insulators 38 and 31, are shown in Fig. 1, and a third or which, the insulator 36a, is shown in Fig. 2. The upper ends of these insulators form with screws 39, spacers 49 and top plate 40, a clamp for an intermediate plate 5i]. The plate it is suspended from three rods 4!, 42, and 43, which in turn are carried by a yoke 64 which threadedly engages a feed screw 55. The feed screw 45 extends through an upper plate 46 of the housing and is driven through gears 41 and 48 by the motor 36.

In order that the upper electrode or capacitor plate'ld may be independently adjustable, it will be observed, Fig. 2, that the respective corners thereof are cut away as indicated at 5! to provide clearance around the supporting insulators 36 and 36a. The electrode I3 is itself supported by means of tour insulators two of which, the insulators 54 and 54a, are shown in Fig. 2, and a third, the insulator 53, being shown in Fig. 1. These insulators at their upper ends are secured to a plate 55 supported by an adjusting mechanism which includes a threaded member 56 and a threaded yoke 51' of construction identical with the one described ior the adjustment of the electrode 12. The lower ends of the insulators are secured to the electrode 53 by countersunk screws (not shown) in the same manner as for the insulators associated with the electrode-plate [2. The plate 55 and the electrode it are moved upwardly or downwardly with respect to electrode l2 by suitable manual or automatic energization of the motor 3i which, through the gears 58 and 59, drives the threaded member 56. One end of a flexible conductor 60 is fastened to a selected position on the inductor l5 and the other end is secured to the movable electrode l3, as by screws.

In operation, the load ill comprising material to be treated or raised in temperature is placed upon the tray-electrode l I and is moved into the cabinet so as to be substantially centered beneath the electrode l2. This material may comprise plastic preforms or material whose shape is to be altered after the generation of heat therein and under the influence of applied pressure. With the material in place, the motor 30 is energized in a direction in unison to lower the assembly which includes the electrode 12, the motor 31, and its associated sub-assembly including the upper electrode l3. When the electrode 12 engages the work, the motor 35 will be deenerized either manually or automatically by operation of suitable means, as a limit switch, not shown.

When the electrode l2 engages the work, the capacitor plate or electrode l3 preferably will be spaced a substantial distance from electrode l2 for application of a relatively low voltage to the work disposed between electrodes ll and I2. Before the high-frequency generator is energized downward pressure may be applied to the load by electrode l2. This pressure may be due to the weight of the sub-assembly, the actuating rods ll-t3 being effective to lift the sub-assembly and to be lowered so that the enlarged ends are free of plate fill. In consequence, the weight of the sub-assembly is applied to the load. lhe downward pressure may be increased by adding weight to the plate 40 or by using a weight suspended from a lever arranged to press downwardly on the plate 45. The applied pressure serves to smooth out irregularities in the surface of the work which might otherwise cause arcing under normal operation by reason of small air gaps between the work and the electrode l2. The applied pressure not only flattens out irregularities and minimizes arcing but it also minimizes swelling and distortion of the work during the heating operation.

With the material to be heated under pressure of desired magnitude, and the electrode [3 in a position of desired minimum capacity, corresponding with a reduced voltage applied to the material to be heated, the oscillator, including the valve 17, will be energized to apply high-irequency energy to the load. The motor 31 will then be energized in a direction to increase the capacitance between electrodes I2 and I3 and to raise the voltage applied to the load. When the output current reaches a predetermined value, such, for example, as may be indicated by a distinctively colored area l9a on the face of the meter IS, the progressive increase in the voltage and capacitance may be terminated.

As soon as the desired heating or treating time has elapsed, the oscillator or valve I! will be deenergized and the motor 35 energized to raise in unison the electrode l2 and associated assembly, including electrode l3, out of engagement with the material which has been heated. The motor 3| may also be energized to raise the capacitor plate [3 a predetermined amount preparatory to the next heating operation. The drawer-electrode l I may then be withdrawn from the cabinet together with the load or charge carried thereby.

During the heating operation, the motor 3| may be energized to vary the capacitance between electrodes l3 and I2 and so control the rate of heating of the load. This control may be automatic in response to magnitude of the plate current of the high-frequency generator, and may comprise a system of the type disclosed and claimed in my co-pending application, Serial No. 597,048, filed June 1, 1945, and entitled Highfrequency treating system. Or, the strap or flexible conductor 60 may be secured to the elecscorers trode 2 and the moto .1. automatic com trolled in the same manner as described in my afores id appli a i n spe c y w th a variable airspace between the work and the electrode 1;.

-W-hile ,a preferred embodiment of my invention has been described, it is to be understood that ,further modifications of the invention may be made without departing from the scope of the appended claim What is claimed is:

Ahigh-frequency heating system comprising a hi h-frequency generator having an output circult, two variable capacitors in series with each other in said output circuit and compriiing three spaced, parallel, plate-like electrodes, means car.- ri d by a second of said electrodes for supporting a first of said electrodes, means for moving the first and second of said electrodes in unison to vary their parallel Spacing with respect to the third of said electrodes to accommodate dielectrio objects to be heated between said second and third electrodes and without variation of the capacity between said first and second electrodes, and means for. moving the first of said electrodes relative to said second electrode to vary the capacity between said first and second electrodes so to -vary the radio-irequency voltage applied to said objects and without variation of the spacing between said second and third electrodes.

2. A high-frequency heating apparatus comprising a work tray forming one electrode, two movable parallel electrodes spaced one above the other over said tray, adjustable supporting structure carried by one movable electrode for adjustably supporting the other movable electrode, means for raising and lowering said two electrodes in unison, means for operating said structure independently to raise and lower the upper of said two electrodes, a high-frequency generator having an output circuit, and means connecting said circuitto said work tray and to the upper of said two electrodes.

3. A dielectric heating apparatus comprising three electrodes arranged in faceeto-face relation to providetwov electric capacitors in series-circuit relationship, one of the outside ones of said electrodes being stationary, the intermediate one of said electrodes and said stationary electrode being arranged to receive therebetween dielectric material to be heated by an electric field, a source of high-frequency electrical energy, means connecting said source and said capacitors in series including connections to said stationaryelectrodeand to the other of said outside electrodes, and adjustable supporting structure operable to vary the positions of said last-mentioned outside electrode and of said intermediate electrode relative to each other and to said stationary electrode, thereby to vary the capacitances between said intermediate electrode and said outside electrodes.

4. A dielectric heater comprising a first platelike electrode, a second plate-like electrode parallel to and forming a capacitor with said first electrode, a supporting member for said second electrode, insulators secured to and extending between said member and said second electrode, driving means connected to said member for moving said second electrode relative to said first electrode along a path generally normal to the plane thereof, a third parallel plate-like electrode forming a capacitor with said second electrode and having openings through which said insulators extend, insulated dIiViIlg means for moving said third electrode toward and away from said second electrode along a path generally normal to the planethereof, and means for connecting between said third electrode and said first electrode a source of high-frequency electrical energy with said capacitors in series therewith.

5. In a dielectric heater the combination of a first plate-like electrode, a second plate-like elec trode spaced therefrom for disposition therebetween of material to be heated, adjustable means for bodily moving said second electrode toward and away from said first electrode along a path normal to the plane thereof and comprising a supporting member movable with said second electrode, elongated insulators connected between said member and said second electrode and a motor-driven positioning means connected to said supporting member, a second adjustable means supported from said member, a third plate-like electrode, means including insulators connected to said third electrode and movable by said second adjustable means to. vary the position of said third electrode relative to said second electrode, and means for connecting said first electrode and said third electrode to a source of high-frequency electrical energy to provide a pair of capacitors in series. therewith.

6. The combination set forth in claim 5, in. which said electrodes are of substantially the same area except that the corner portions of said third electrode are cut away to make room for the. insulators of said first adjustable means.

7. In a dielectric heating apparatus, the come bination of a first plate-like electrode, a unitary structure movable relative thereto and including a second plate-like electrode and means support ing said second electrode in parallel insulated capaeitive relation with said first electrode, said first and second electrodes bein arranged to re'-- ceive therebetween dielectric material to be heat-- ed by an electric field, means for moving said unitary structure to vary the parallel spacing of said second electrode relative to said first electrode, a third plate-like electrode carried by said movable unitary structure in parallel insulated capacitive relation with said second electrode, a source of high-frequency electrical energy, means connecting said source to said first and third electrodes to provide two capacitors in series with said source, said third electrode being movabl to var the capacitance between said second and third electrodes, and means for moving said third electrode relative to said second electrode independently of relative movement between said second and first electrodes.

8. In a dielectric heating apparatus, the combination of a first plate-like electrode, a unitary structure movable relative thereto and including a second plate-like electrode and means support ing said second electrode in parallel insulated capacitive relation with said first electrode, said first and second electrodes bein arranged to receive therebetween dielectric material to be heated by an electric field, driving means for moving said unitary structure to vary the parallel spacing of said second electrode relative to said first electrode, a third plate-like electrode carried by said movable unitary structure in parallel insulated capacitive relation with said second electrode, a source of high-frequency electrical energy, means connecting said source to said first and third electrodes to provide two capacitors in series with said source, said third electrode being movable to vary the capacitance between said second and third electrodes, and driving means carried by said movable unitary structure and operable to effect movement of said third electrode relative to said second electrode independently of relative" electrode disposed in capacitive relationship and arranged to receive therebetween dielectric material to be heated by an electric field, means operable to efiect relative movement between said electrodes and to control the application of pressure on material disposed therebetween, .a source ofhigh-frequency electrical energy connected to said first electrode, a third plate-like electrode connected to said source of energy and disposed in capacitive relation-chip with said second electrode on the opposite side of the latter from said first electrode to form two capacitors in :series wtih said source, and means operable to effect movement of said third electrode relative to said second electrode independently of relative movement between said first and second electrodes, thereby to vary the capacitance between said second and third electrodes.

10. A high-frequency dielectric heating apparatus comprising a first plate-like electrode, a unitary structure movable relative thereto and including a second plate-like electrode and means supporting the latter in parallel insulated capaci-- tive relation with said first electrode, said first and second electrodes being arranged to receive therebetween dielectric material to be heated by an electric field, driving means for moving said unitary structure to vary the spacing of said second electrode relative to said first electrode and after engagement of said second electrode with said dielectric material for controlling the application by said unitary structure of a substantial positive pressure on said material engaged by said first and second electrodes, a sub-assembly wholly supported by said movable unitary structure and including a third plate-like electrode supported in parallel insulated capacitive relation with said second electrode on the opposite'side of the latter from said first electrode, said subassembly including driving means for varying the spacing of said third electrode relative to said second electrode so as to var the capacitance between the second and third electrodes independently of variation of the spacing between said first and second electrodes, and a source of high-frequency electrical energy connected to said first and said third electrodes the two capacito'rs between said electrodes being in series with said source. 11. A high-frequency dielectric heating apparatus comprising a first plate-like electrode, a source of high-frequency electrical energy connected therewith, a unitary structur movable relative to said electrode and including a second plate-like electrode arranged in capacitive relation with said first electrode for accommodation of dielectric material to be heated by an electric field between said first and second electrodes, said movable unitary structure als including a supporting member and compression insulators rigidly joining said second electrode to said member, motor-driven means for moving said unitary structure relative to said first electrode and after engagement of said second electrode with said material for controlling the application by said unitary structure of a substantial positive pressure on said material engaged by said first and second electrodes, and a subassembly wholly supported by said movable unitary structure and including a third plate-like electrode supported in insulated capacitive relation with said second electrode, said third electrode being disposed between said second electrode and its said supporting member and being connected with said source of electrical energy, said sub-asssembly also including motor-driven means operable to vary the spacing of said third electrode relative to said second electrode so as to vary the capacitance between said second and third electrodes independently of variation in the capacitance due to positioning of said second electrod relative to said first electrode.

WILFRID L. ATWOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Electronics, vol. 18, No. 2, February 1945, pages;

114 and 115. 

